1. Field of the Invention
This invention relates to a pneumatic tire, and more particularly to an improvement of a tread rubber structure suitable for use in a pneumatic tire for heavy load vehicles such as trucks, and buses and the like mainly running on both good and bad road surfaces.
2. Related Art Statement
In the conventional pneumatic tire, the tread rubber is composed of a single rubber layer or two different rubber layers laminated one upon the other in radial direction of a so-called cap and base structure. However, when such a pneumatic tire is used on a running road including a fairly high ratio of each of both good and bad surface, the appearance (number of injuries on tread surface) and wear resistance of the tire can not simultaneously be maintained at higher level because there is caused a large difference in the appearance between the central region and the either side region of the tread. Also, the wearing state of the tread becomes ununiform. That is, when the tire is run on the above road for a long period of time, the appearance of the central region of the tread is considerably degraded as compared with that of the either side region, while the wear resistance of the either side region is considerably poorer than that of the central region.